(1) Field of the Invention
The present invention relates to a method of developing various photosensitive materials. More particularly, the invention is concerned with an automatic developing method for positive working photosensitive lithographic printing plates
(2) Description of the Prior Art
A method for developing a photosensitive lithographic printing plate (hereinafter referred to as "PS plate") by an automatic developing apparatus has been widely used. In this conventional method, an imagewise exposed PS plate which has been transferred to the developing section is dipped in a developing solution or the developing liquid is sprayed onto the surface of the photosensitive layer of the PS plate, while it is being conveyed, so as to dissolve or swell either the exposed or non-exposed region of the photosensitive layer, and then rubbing the photosensitive material with a brush in order to remove the non-image portion of the photosensitive layer In this method, a predetermined amount of the developing liquid is charged in the tank of the developing apparatus and recirculated by a pump so as to be used repeatedly, so that the developing ability of the developing liquid is gradually degraded with use. If the developing liquid is used too long, the ability of the developing liquid to dissolve the non-image portion of the photosensitive layer is impaired, resulting in "development failure". This development failure is attributable to the following reasons: namely, a phenomenon referred to as "processing exhaustion reduction" which is attributable to the consumption of the effective components in the developing liquid by the component eluted from the photosensitive layer; and a phenomenon called "secular exhaustion reduction" which is experienced when the developing liquid is an alkali solution, due to neutralization reaction caused by absorption of carbon dioxide gas in the air or, alternatively, experienced when the effective component of the developing agent is alcohol, due to evaporation of the latter.
In order to protect the developing liquid from processing exhaustion reduction and secular exhaustion reduction, methods have been proposed for continuously or intermittently supplying supplementary developing liquid in accordance with the processing rate, as described in Japanese Patent Application (OPI) No. 144502/1975 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), U.S. Pat. No. 4,259,434 and British Pat. No. 2,046,931. In these methods, however, the composition of the developing liquid is inevitably changed from that of the initial or fresh developing liquid, although processing exhaustion reduction and secular exhaustion reduction are compensated for by the supply of the supplementary developing liquid. This means, in a strict sense, that the quality of the development differs in every developing cycle, with the result that the performance of the photosensitive material after the development does not become constant.
Another method is also known in which the developing liquid is supplied to an imagewise exposed photosensitive material in an amount required for each developing cycle, and the surface of the photosensitive material is rubbed with a brush or a sponge so that the nonimage region of the photosensitive layer is removed, as disclosed in, for example, U.S. Pat. No. 4,222,656. This method, however, causes incomplete development, so that the non-image portion is liable to be scummed during printing, even though the development appears to be satisfactory, particularly when this method is applied to the development of a PS plate.